Oxidation catalysts

ABSTRACT

A vapor phase catalytic oxydehydrogenation process for the conversion of a steam of mixed isomeric isoamylenes, methyl butanols or mixtures thereof to isoprene with relatively short contact times at a reactor temperature in the range of 500° F. to 1100° F. at from 0.5 to about 10 atmospheres pressure. The catalysts comprise an alkali metal as an essential catalytic ingredient.

CROSS REFERENCE TO RELATED APPLICATIONS

.Iadd.This is a continuation of application Ser. No. 713,024, filed Aug.9, 1976, now abandoned. .Iaddend.

This application is a continuation-in-part of our copending and nowabandoned application Ser. No. 794,469 filed Dec. 30, 1968.

BACKGROUND OF THE INVENTION

The catalytic oxydehydrogenation of olefins for the production ofbutadiene and isoprene has been the subject of continued interest formany years. The prior art encompasses catalysts consisting of elementswhich appear to cover the entire spectrum of the Periodic Table.Particular oxydehydrogenation catalysts are disclosed in U.S. Pat. Nos.2,991,321; 2,991,322; 3,067,272; 3,110,746; 3,119,111. An all-importantrequirement in the commercial production of any chemical by catalyticoxidation is that the catalyst exhibit not only high conversion butextremely high selectivity for long periods of time. The foregoingpatents, drawn to oxydehydrogenation catalysts, are disclosed to begenerally effective in several reactions. The instant catalyst on theother hand, is particularly and unexpectedly effective in the conversionof isoamylenes, methyl butanols, or diisoamylene to isoprene, despitethe presence of an alkali metal as an essential ingredient, and arelatively high content of Group VIII Fourth Period element.

This invention relates to oxydehydrogenation catalysts consistingessentially of an alkali metal as an essential catalytic ingredient incombination with oxides of bismuth, molybdenum and iron. The instantalkali metal containing catalyst is an improvement over prior artcatalysts in that it is particularly suited to the catalyticoxydehydrogenation of isoamylenes, methyl butanols or mixtures thereofto isoprene.

It is noteworthy that, in general, a catalyst particularly effective inone oxydehydrogenation reaction is conspicuously unable to perform aswell in another. For example, an oxydehydrogenation catalyst containingthe oxides of bismuth, molybdenum, iron and nickel is disclosed in U.S.Pat. No. 3,414,631, and it is particularly efficient in theoxydehydrogenation of butene to butadiene but significantly lesseffective in the conversion of isoamylenes to isoprene. This peculiarand unexplained preference of a catalyst for one reaction over anotherapparently analogous one, is reflected and focused by the absence ofexamples disclosing analyses of the products of reaction in a number ofprior art disclosures. In any event, there is significant utility of theinstant invention in the catalytic oxidation of olefins to unsaturatedaldehydes and acids, and for the catalytic ammoxidation of olefins tounsaturated nitriles.

DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION

The alkali metal oxide-bismuth oxide-molybdenum oxide-iron oxide basecatalyst disclosed herein is referred to as a mixture of metal oxides,but this is not to be construed as meaning that the catalyst is composedeither in whole or in part of only these compounds. The proportions ofalkali metal, bismuth, molybdenum and the Group VIII Fourth Periodelement in the catalyst may vary within the ranges describedhereinafter. Preferred alkali metals are potassium, cesium and rubidium.Preferred alkaline earth metals are magnesium, calcium, strontium andbarium. Additionally, the instant catalyst may include promoters fromGroup V and particularly phosphorus, arsenic and antimony.

The unsupported catalyst of the instant invention gives excellentresults. In a commercial reactor, for economic reasons, it might bedesirable to use a catalyst support which may constitute from 3 percentto 99 percent, and preferably between 5 percent and 95 percent by weightof the finished catalyst. Any known catalyst support such as alumina,pumice, silicon carbide, zirconia, titania, silica, alumina-silica, andthe inorganic phosphates, silicates, aluminates, borates and carbonatesstable under the reaction conditions may be used.

In the preparation of the promoted catalysts useful in this invention,the metal oxides can be blended together or can be formed separately andthen blended or formed separately or together in situ. Promoter oxidesare preferably incorporated into the alkalimetal-bismuth-molybdenum-iron base catalyst by blending into the gelbefore calcining or by blending into the oven-dried base catalyst beforecalcining. A preferred manner of incorporating promoter elements is bychoosing a water-soluble salt of the promoter element, forming anaqueous solution of the salt, and mixing the solution with a solution ora suspension of the base elements or salts thereof. Optionally, thepromoter elements may be incorporated by the use of soluble complexsalts or compounds with the desired base elements which upon calcinationwill yield the desired ratio of the elements in the finished catalyst.

The alkali metal may be introduced into the catalyst as an oxide or asany salt which upon calcination will yield the oxide. Preferred saltsare the nitrates which are readily available and easily soluble.

Bismuth may be introduced into the catalyst as an oxide or as any saltwhich upon calcination will yield the oxide. Most preferred are thewater-soluble salts which are easily dispersible within the catalyst andwhich form stable oxides upon heat-treating. The most preferred salt forintroducing bismuth is bismuth nitrate.

To introduce the iron component into the catalyst one may use anycompound of iron which, upon calcination, will result in the oxides. Aswith the other elements, water-soluble salts are preferred for the easewith which they may be uniformly dispersed within the catalyst. Mostpreferred is ferric nitrate. Cobalt and nickel are similarly introduced.

To introduce the molybdenum component, any molybdenum oxide such as thedioxide, trioxide, pentoxide, or sesquioxide may be used; more preferredis a hydrolyzable or decomposable molybdenum salt such as a molybdenumhalide. A preferred starting material is ammonium heptamolybdate.

The alkali or alkaline earth metals may be introduced into the catalystin the form of water-soluble salts or insoluble carbonates, hydroxidesand the like, which result in the oxides upon heat-treating. Whenphosphorus is desired in the catalyst it may be introduced as phosphoricacid, or as an alkali or alkaline earth phosphate, particularly if it isdesired to neutralize the solution and at the same time introduce thedesired elements as phosphates. Arsenic may be introduced asorthoarsenic acid, and antimony may be introduced as a slurry of hydrousantimony oxide formed in situ from the metal in nitric acid, or by theaction of boiling nitric acid on antimony oxide. Other promoter elementsmay be introduced, starting with the metal, oxidizing the metal with anoxidizing acid such as nitric acid, and then incorporating the nitrateinto the catalyst. Generally, the nitrates are readily available andform a very convenient starting material.

Other variations in starting materials will suggest themselves to oneskilled in the art, particularly when the preferred starting materialsmentioned hereinabove are unsuited to the economics of large-scalemanufacture. In general, any compounds containing the desired catalystcomponents may be used provided that they result, upon heating to atemperature within the range disclosed hereinafter, in the oxides of theinstant catalyst. Proper selection of the promoter elements and theproportions of the elements present in the catalyst will influence theselectivity of particular oxydehydrogenation reactions. Thus, in somecases one might use a relatively high amount of potassium and a loweramount of magnesium with a phosphorus promoter, while in other cases onemight use a minor quantity of a cesium promoter with a relatively highamount of barium without any phosphorus.

The catalytic activity of the novel catalyst embodied in the presentinvention is enhanced by heating the catalyst at an elevatedtemperature. Preferably the catalyst mixture is dried and heated at atemperature of from 500° F. to 1250° F., more preferably at about 800°F. to 1150° F. for from 2 to 24 hours. If the activity-selectivityrelationship is not satisfactory, the catalyst can be furtherheat-treated at a temperature above about 800° F. but below atemperature deleterious to the catalyst at which it is grosslydecomposed, preferably in the range from about 800° F. to about 1400° F.for from 1 to 48 hours, in the presence of oxygen or anoxygen-containing gas such as air.

There appears to be no readily discernible correlation betweenactivation temperature and the time required to effect activation. Thesufficiency of activation at any given set of conditions is ascertainedby a spot test of a sample of the material for catalytic activity.Activation is best carried out in an open chamber, permittingcirculation of air or oxygen, so that any oxygen consumed will bereplaced.

It has also been found that some of the instant catalysts can be furtheractivated by subjecting heat-treated catalyst to a reducing atmospherefor a period of from about 1 hour to about 48 hours at a temperature inthe range from about 400° F. to about 1250° F. This reducing treatmentis conveniently accomplished by flowing a reducing gas such as ammonia,hydrogen or the like over the catalyst. It was found that catalyststreated with a reducing gas gave higher conversions to isoprene aftersome time, though during an initial short period of time, conversionswere actually lower than those given by the same catalysts not subjectedto the reducing treatment.

The instant catalyst comprising an alkali metal as an essentialcatalytic ingredient with the combined oxides of bismuth, molybdenum andiron may be defined by the following formula:

    Bi.sub.a Fe.sub.b Mo.sub.c Q.sub.d R.sub.e T.sub.f M.sub.g O.sub.x

wherein

Q is an alkali metal,

R is an alkaline earth metal,

T is phosphorus, arsenic or antimony,

M is cobalt or nickel; and

wherein

a, b and c are numbers in the range 0.1 to 12,

d is a number from 0.1 to 8,

e is a number from 0 to 8,

f is a number from 0 to 6,

g is a number from 0 to 12,

x is a number determined by the valence requirements of the otherelements present.

The process of the instant invention is specifically concerned with theconversion of isoamylenes, methyl butanols or mixtures thereof toisoprene. This process involves passing a mixture of isoamylenes or anyparticular isomeric isoamylene, and a molecular oxygen-containing gassuch as air, in the presence or absence of a diluent such as steam,carbon dioxide, nitrogen or other inert gas at relatively hightemperatures over a catalyst of a composition described hereinabove.

It is a noteworthy feature of the instant process that a mixed stream ofisomeric isoamylenes and methyl butanols, without regard to the molarbalance of isomers and methyl butanols, may be fed to the reactor withsubstantially the same results in conversion. In all of the exampleappended hereto, the more easily converted 3-methyl butene-1 wasdeliberately excluded from the feed, which consisted of a mixture of2-methyl butene-1 and 2-methyl butene-2. The alcohol utilized in theexamples was t-amyl alcohol although 2-methyl butanol-3,3-methylbutanol-1, and 2-methyl butanol-1 can also be converted.

The above-described catalysts are active at temperatures in the rangefrom about 500° F. to about 1000° F., and a preferred range foroperation is between 650° F. and 900° F. In this temperature range thecatalysts exhibit exceptional activity and selectivity.

The pressure at which the instant process is usually conducted is aboutatmospheric, although pressures of from slightly below atmospheric up toand above 3 atmospheres are operable.

The apparent contact time employed in the instant process may be withinthe range of 0.01 to 20 seconds, and for good selectivity and yields acontact of from 0.1 to 10 seconds is preferred.

Molar ratios of isoamylenes to air may vary from about 1:1 to about1:20. Ratios near the higher limit usually make for poor selectivity andratios near the lower limit tend to decrease catalyst activity. Thepreferred molar ratio of isoamylenes to air is in the range of about 1:1to 1:10. It may be advantageous to include gases such as steam, carbondioxide or nitrogen in addition to the nitrogen contained in the air fedto the reactor. However, for economic reasons it is usually notdesirable to add more than 10 volumes of diluent gas for each volume ofisoamylene in the feed.

The reactor employed for the conversion of isoamylenes, methyl butanolsor mixtures thereof to isoprene in the instant invention may be afixed-bed reactor, or a fluid-bed reactor. Changes in the physicalcharacteristics of the catalyst described above, particularly to suiteither the fluid-bed or the fixed-bed reactor, may be made according toknown methods familiar to those skilled in the art. The particularreactor employed in the instant process for the examples appended heretowas a standard reactor with a fixed catalyst bed. The catalyst volumewas about 20 cc., and the catalyst mesh size was 20-35 Tyler screenmesh. The gases were metered to the reactor with rotameters. Thereaction products were analyzed by means of a gas chromatograph Thecolumn employed was a one-fourth (1/4) inch diameter by 4 meter columnpacked with 20 percent orthonitrophenetole on Chromosorb W forhydrocarbons. Carbon dioxide and carbon monoxide were determined bymeans of a Fisher gas partitioner, using hexamethyl phosporamide andmolecular sieve columns in series. Isoamylenes, methyl butanols andisoprene were analyzed by passing the reactor effluent gases over asolid drying agent and then into a gas sampling valve which was openedperiodically for gas chromatographic analysis.

Example 1

A specific catalyst was made as follows: 36.4 grams bismuth nitrate,Bi(NO₃)₃ ·5H₂ O, were dissolved in 700 ml. dilute nitric acid taken in alarge beaker. 7.6 grams potassium nitrate, KNO₃, 120 grams cobaltousnitrate, Co(NO₃)₂ ·6H₂ O, and 182 grams ferric nitrate,

    Fe(NO.sub.3).sub.3 ·9H.sub.2 O

were all added to the solution and also dissolved. 8.65 grams phosphoricacid (85 percent) were added to the solution while it was continuouslystirred. 159 grams ammonium molybdate, (NH₄)₆ Mo₇ O₂₄ ·4H₂ O, weredissolved in a small quantity of water and slowly added to the foregoingacidic solution. Precipitation wes instantaneous. The solution wasconstantly stirred and heated over a hot plate until the entire massgelled. The gel was spooned out into trays and dried in a conventionalconvection oven at 130° C. for 16 hours. The dried mass was thencalcined in air at 800° F. for 16 hours. A final heat-treatment in airat 1000° F. for 3 hours was given the catalyst prior to loading into thereactor.

Other catalyst compositions were prepared in a similar manner using, forconvenience, water-soluble salts of the elements desired in the finalcomposition, though as has been disclosed hereinbefore, the use ofwater-soluble salts is not essential.

In Table I appended hereto, various catalysts, prepared in a mannersimilar to that described in Example 1 above, are effective in themanufacture of isoprene under the tabulated process conditions. All runsin Table I were made in a fixed-bed reactor at 750° F. with a feedconsisting of a mixture of 2-methyl butene-1 and 2-methyl butene-2diluted with nitrogen, and the molar ratio of air:isoamylenes:nitrogenwas about 4:1:4. Particular physical characteristics such as surfacearea, density, particle size, and the like may be obtained by ajudicious choice of proportions of catalyst elements, the ratio ofcatalyst to catalyst support, and the manner in which catalyst ispreliminarily calcined prior to its final heat treatment, all of whichcharacteristics may be modified to suit the particular reactor andpredetermined conditions of reaction in accordance with known skills,and none of which physical characteristics is specifically tabulatedherein.

The appended Table II lists various promoted catalysts with and withouta catalyst support under varying temperature of reaction, contact time,and air:nitrogen ratios.

The appended Table III is a comparison of a prior art catalyst and thatof the instant invention. It will be noted that the latter contains analkali metal as an essential catalytic ingredient.

The appended Table IV lists runs utilizing the instant catalyst on somepreferred supports.

In the appended Table V, two runs are shown utilizing a catalystconsisting of 60 percent Fe₉ Bi₃ PMo₁₂ O_(x) ·K₂ SO₄ and 40 percentTiO₂, wherein x is a number taken to satisfy the oxygen requirements ofthe elements in the catalyst. The reactor was a fixed bed, and thecontact time was 4 seconds. In one case a t-amyl alcohol feed was used,while in the other an equimolor mixture of t-amyl alcohol and 2-methylbutene-2 was used.

In all of the examples tabulated in the tables hereinbelow, smallquantities of by-products are formed which are not specificallyidentified (or quantified in the tables) and have been disregarded inthe calculations. These by-products may be oxidation products such asthe aldehydes and acids and are usually present as relatively highmolecular weight condensation products with an oily appearance.

In the examples listed hereinbelow, the following definitions areemployed: ##EQU1##

From the foregoing description of the manner in which the experimentalruns were made, it will be apparent that there were no provisions formany process steps which would be engineered into a commercial unit. Forexample, in a commercial reactor, the effluent would preferably becooled by indirect heat exchange with the incoming feed and thenscrubbed with water or dilute caustic to neutralize traces of organicacids present, to inhibit the formation of oily polymeric by-products,and to condense and remove steam. If air is used to supply the oxygen,the remaining mixture is preferably compressed and scrubbed with oil toseparate the hydrocarbons from the nitrogen, carbon dioxide and carbonmonoxide. The hydrocarbon may be stripped from the oil and subjected toan extractive distillation or a copper ammonium acetate treatment in theknown manner to separate and recover the diolefin. Unreacted isoamyleneswould be recycled to the reactor from the recovery section, and it isnot essential that the recycle stream be pure isoamylenes. It cancontain carbon dioxide, carbon monoxide, nitrogen and steam since thesegases would serve only as diluents.

In the claims below, the term "consisting essentially of" is meant toinclude the main elements, namely, alkali metal, bismuth, molybdenum andiron, and the specified promoters where applicable, but is not meant toexclude small amounts of other elements, the presence of which may beincident to the quality, origin or particular processing of rawmaterials used to manufacture the instant catalyst. It will be apparentto thse skilled in the catalytic oxidation art that embodiments of theinvention, other than those specifically described for illustrativepurposes, may be evolved and that modifications in these specificembodiments may be made without departing from the spirit and scope ofthe invention as expressed above and as defined in the appended claims.

                                      TABLE I                                     __________________________________________________________________________                     Contact                                                                            Percent per pass                                                                         Total                                                         time,                                                                              conversion to                                                                            percent                                                                             Selectivity,                           Example                                                                            Catalyst    secs.                                                                              Isoprene                                                                           CO.sub.2                                                                         CO conversion                                                                          percent                                __________________________________________________________________________     1   KFe.sub.4 BiMo.sub.12 Co.sub.5.5 O.sub.x                                                  3.2  50.2 6.26                                                                             1.30                                                                             57.7  87.0                                    2   K.sub.0.28 Fe.sub.4 Bi.sub.3 PMo.sub.12 O.sub.x                                           3.8  33.8 5.53                                                                             1.03                                                                             43.0  78.6                                    3   KFe.sub.4 Bi.sub.3 PMo.sub.12 O.sub.x                                                     3.8  44.6 6.33                                                                             1.04                                                                             53.4  83.5                                    4   K.sub.2 Fe.sub.9 Bi.sub.3 ; PMo.sub.12 O.sub.x                                            3.5  50.7 6.73                                                                             1.40                                                                             60.7  83.4                                    5   K.sub.3 Fe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x                                              3.7  47.5 6.42                                                                             0.92                                                                             57.5  82.7                                    6   K.sub.4.5 Fe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x                                            3.8  33.0 7.77                                                                             1.12                                                                             41.8  78.9                                    7   K.sub.6 Fe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x                                              3.7  18.5 5.13                                                                             0.61                                                                             24.7  74.8                                    8   RbFe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x                                                    3.7  53.6 3.95                                                                             0.90                                                                             61.5  87.2                                    9   Li.sub.0.1 Fe.sub.4 Bi.sub.3 PMo.sub.12 O.sub.x                                           3.9  36.0 7.38                                                                             1.32                                                                             45.5  79.1                                   10   Li.sub.2 Fe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x                                             3.8  34.5 7.08                                                                             1.30                                                                             42.8  80.5                                   11   K.sub.3 Fe.sub.9 Bi.sub.2 PMo.sub.12 O.sub.x                                              3.6  51.1 5.78                                                                             0.85                                                                             59.9  85.3                                   12   CsFe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x                                                    3.6  52.4 5.17                                                                             0.82                                                                             61.5  85.2                                   13   CsFe.sub.4 Bi.sub.3 PMo.sub.12 O.sub.x                                                    3.5  60.4 5.95                                                                             1.00                                                                             71.5  84.4                                   14   K.sub.2 Fe.sub.4 BiPMo.sub.12 O.sub.x                                                     3.4  53.2 7.28                                                                             1.29                                                                             61.8  86.2                                   15   K.sub.4 Fe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x                                              3.6  43.7 6.98                                                                             1.09                                                                             53.1  82.4                                   16   K.sub.2 Fe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x                                              0.2  54.1  6.7                                                                              1.5                                                                             57.7  87.0                                   17   NaFe.sub.4 Bi.sub.3 PMo.sub.12 O.sub.x                                                    2.5  32.9  6.2                                                                              1.3                                                                             40.4  81.5                                   18   K.sub.0.1 Fe.sub.2 Bi.sub.0.5 Sb.sub.0.8 Mo.sub.6 O.sub.x                                  .5  49.8  5.7                                                                              1.4                                                                             56.9  88.0                                   __________________________________________________________________________

                                      TABLE II                                    __________________________________________________________________________    Ex-                               Air/N.sub.2 *                                                                      Contact         Total                                                                             Percent            am-                         Temp.,                                                                              mole time,                                                                              Percent conversion                                                                       con-                                                                              selec-             ple                                                                              Catalyst                 °F.                                                                          ratio                                                                              secs.                                                                              Isoprene                                                                           CO CO.sub.2                                                                         version                                                                           tivity             __________________________________________________________________________                                  700   6/2.5                                                                            4     6.0 0.3                                                                               1.8                                                                              8.1                                                                              74                 19 82.5% KCo.sub.2 Ni.sub.0.5 Fe.sub.0.5 Bi.sub.0.5 AsMo.sub.12 O.sub.x.17       .5% SiO.sub.2              750   6/2.6                                                                            4    24.3 1.7                                                                              9.0                                                                              32.0                                                                              76                    support                    800   6/2.6                                                                            4    35.2 1.8                                                                              12.0                                                                             49.0                                                                              71.9                                             650   6/2.6                                                                            4     7.5 1.8                                                                              8.0                                                                              17.3                                                                              43.4               20 82.5% KNi.sub.10.5 FeBi.sub.0.5 Sb.sub.0.5 Mo.sub.12 O.sub.x.17.5%            SiO.sub.2 support          700   6/2.5                                                                            4    32.3 3.0                                                                              11.8                                                                             47.1                                                                              68.5                                             750   6/2.6                                                                            4    36.4 2.8                                                                              11.8                                                                             51.0                                                                              71.3                                             700 6.2/3.7                                                                            1    15.2 1.1                                                                               5.4                                                                             21.7                                                                              70.0               21 100% KNi.sub. 10.5 FeBi.sub.0.5 Sb.sub.0.5 Mo.sub.12 O.sub.x                                             750 6.3/3.8                                                                            1    31.7 2.0                                                                              10.4                                                                             44.1                                                                              71.9                                             800 6.6/3.9                                                                            1    33.2 1.8                                                                              12.6                                                                             47.6                                                                              69.7                                             700 5.4/3.2                                                                            1     9.6 0.8                                                                               3.4                                                                             13.8                                                                              69.6               22 80% KCo.sub.0.5 Fe.sub.4 BiPMo.sub.12 O.sub.x.20% Al.sub.2 O.sub.3            support                                                                                                  750 5.6/3.4                                                                            1    31.7 3.6                                                                               8.3                                                                             43.6                                                                              72.6               __________________________________________________________________________     *Per mole isoamylene.                                                    

                                      TABLE III                                   __________________________________________________________________________                              Contact                                                                            Percent per pass                                                                         Total                                                                             Percent                                         Molar ratio                                                                         Temp.                                                                             time conversion to-                                                                           con-                                                                              selec-                          Example                                                                            Catalyst   air/N.sub.2.sup.1                                                                   (°F.)                                                                      (secs.)                                                                            Isoprene                                                                           CO.sub.2                                                                         CO version                                                                           tivity                          __________________________________________________________________________    23   Bi.sub.2 FeMo.sub.4.5 O.sub.x.sup.2                                                      4.02/3.8                                                                            750 2    25.9 8.73                                                                             1.38                                                                             36.01                                                                             72.0                            24   K.sub.0.378 Bi.sub.2 Fe.sub.1 Mo.sub.4.5 O.sub.x                                         4/4   750 2    50.0 6.24                                                                             1.03                                                                             59.90                                                                             83.4                            25   Bi.sub.0.5 Fe.sub.1 Mo.sub.1.34 O.sub.x.sup.2                                            4/4   750 2    28.2 8.57                                                                             1.40                                                                             38.70                                                                             72.8                            26   K.sub.0.1 Bi.sub.0.5 Fe.sub.3 Mo.sub.1.34 O.sub.x                                        4/4   750 2    54.5 5.42                                                                             1.00                                                                             64.00                                                                             85.1                            __________________________________________________________________________     .sup.1 Per mole isoamylenes.                                             

                                      TABLE IV                                    __________________________________________________________________________                                   Molar   Contact                                                                            Percent per                                                                              Total                                                                             Percent                                           ratio,                                                                            Temp.                                                                             time conversion to-                                                                           Con-                                                                              selec-             Example                                                                            Catalyst and support      air/N.sub.2.sup.2                                                                 (°F.)                                                                      (secs.)                                                                            Isoprene                                                                           CO.sub.2                                                                         CO version                                                                           tivity             __________________________________________________________________________    27   65% KFe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x.35% Illinois mineral                (1160).sup.2              4/4 750 4    46.4 6.7                                                                              1.3                                                                              55.3                                                                              82.5               28   80% KFe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x.20% pumice                                                    4/4 750 4    49.6 7.0                                                                              1.3                                                                              60.0                                                                              82.7               29   80% KFe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x.20% Aluminum                                                  4/4sphate                                                                         750 4    41.8 6.2                                                                              1.3                                                                              54.0                                                                              77.4               30   20% KFe.sub.9 Bi.sub.3 PMo.sub.12 O.sub.x.80% Alundum                                                   4/4 750 4    36.2 8.8                                                                              0.7                                                                              44.8                                                                              79.5               __________________________________________________________________________     .sup.1 Per mole isoamylenes.                                                  .sup.2 99% amorphous silica.                                             

                  TABLE X                                                         ______________________________________                                                                     Example 32                                                                    1/1 (molar)                                                         Example 31                                                                              t-amyl alcohol                                                      t-amyl    2-methyl                                         Feed               alcohol   butene-2                                         ______________________________________                                        Air/feed mole ratio                                                                              3.87      3.74                                             Products, percent carbon basis:                                               2-methyl butene-1  14.4      16.6                                             2-methyl butene-2  40.3      45.9                                             Isoprene           41.4      31.2                                             CO.sub.2           5.3       5.5                                              CO                 0.9       0.8                                              Conversion, carbon basis                                                                         45.3      37.6                                             Selectivity        91.4      83.1                                             t-Amyl alcohol conversion, percent                                                               100       100                                              ______________________________________                                         Note-                                                                         Contact time: 4 seconds: 60% Fe.sub.4 Bi.sub.3 Mo.sub.12 O.sub.x.K.sub.2      SO and 40% TiO.sub.3.                                                    

We claim: .[.1. The process for the conversion of isoamylenes, methylbutanols or mixtures thereof to isoprene comprising contacting saidisoamylenes, methyl butanols or mixtures thereof with a molecularoxygen-containing gas over a catalyst consisting essentially of anactivated catalytic oxide complex described by the following formula:isoprene..]. .[.2. The process of claim 1 wherein said molecularoxygen-containing gas is air..]. .[.3. The process of claim 2 whereinthe molar ratio of isoamylenes, methyl butanols or mixtures thereof toair is from 1:0.5 to 1:30..]. .[.4. The process of claim 1 whereinnitrogen is included in the feed stream to said reaction zone..]. .[.5.The process of claim 1 wherein said catalyst is supported on a catalystsupport..].
 6. A catalyst composition consisting essentially of anactivated catalytic oxide complex of an alkali metal, bismuth, iron andmolybdenum as essential catalytic ingredients, and defined by thefollowing formula:

    Bi.sub.a Fe.sub.b Mo.sub.c Q.sub.d R.sub.e T.sub.f M.sub.g O.sub.x

wherein Q is an alkali metal, R is an alkaline earth metal, T isphosphorus, arsenic or antimony, M is cobalt .Iadd.and .Iaddend.ornickel, andwherein a, b and c are numbers in the range 0.1 to 12, d is anumber from 0.1 to 8, e is a number from 0 to 8, f is a number from 0 to6, g is a number from 0 to 12, and x is a number determined by thevalence requirements of the other elements present.
 7. The compositionof claim 6 wherein Q is potassium.
 8. The catalyst composition of claim7 containing phosphorus.
 9. The composition of claim 8 containingcobalt.
 10. The composition of claim 8 containing nickel.
 11. Thecomposition of claim 6 supported on a catalyst support present in arange from 5 percent to 95 percent by weight of the supported catalyst.12. The composition of claim 7 containing cobalt and nickel. .Iadd.13.The composition of claim 7 containing Nickel. .Iaddend. .Iadd.14. Thecomposition of claim 7 containing cobalt. .Iaddend. .Iadd.15. Thecomposition of claim 6 wherein Q is potassium and M is cobalt, andwherein e equals 0, f equals 0, and g is a number larger than 0..Iaddend. .Iadd.16. The composition of claim 7 containing antimony..Iaddend. .Iadd.17. The composition of claim 7 containing arsenic..Iaddend. .Iadd.18. The composition of claim 14 wherein said catalyst issupported on silica. .Iaddend. .Iadd.19. The composition of claim 6wherein Q is cesium. .Iaddend. .Iadd.20. The composition of claim 19containing nickel. .Iaddend. .Iadd.21. The composition of claim 19containing cobalt. .Iaddend. .Iadd.22. The composition of claim 19containing arsenic. .Iaddend. .Iadd.23. The composition of claim 19containing phosphorous. .Iaddend. .Iadd.24. The composition of claim 19containing antimony. .Iaddend. .Iadd.25. The composition of claim 19wherein said catalyst is supported on silica. .Iaddend. .Iadd.26. Thecomposition of claim 6 wherein Q is rubidium. .Iaddend. .Iadd.27. Thecomposition of claim 26 containing nickel. .Iaddend. .Iadd.28. Thecomposition of claim 26 containing cobalt. .Iaddend. .Iadd.29. Thecomposition of claim 26 containing antimony. .Iaddend. .Iadd.30. Thecomposition of claim 26 containing phosphorous. .Iaddend. .Iadd.31. Thecomposition of claim 26 containing arsenic. .Iaddend. .Iadd.32. Thecomposition of claim 26 wherein said catalyst is supported on silica..Iaddend. .Iadd.33. The composition of claim 6 containing nickel..Iaddend. .Iadd.34. The composition of claim 6 containing cobalt..Iaddend. .Iadd.35. The composition of claim 6 wherein Q is sodium..Iaddend. .Iadd.36. A catalyst composition of claim 6 wherein c is 12..Iaddend. .Iadd.37. A catalyst composition of claim 15 wherein c is 12..Iaddend.